Collision aggregation

Even relatively weak attraction between droplets or solid particles in aerosols suffices to create an enhanced collision rate that can change particle-size distributions and overall stability. Think in kT thermal-energy units. Alone, small suspended bodies do a Brownian bop, randomly jiggling from the kT kicks of the air. Should their mutually random paths bring two particles to separations comparable with their size, their van der Waals attraction energy also approaches kT. To previous randomness, attraction adds strength of purpose and increased chance of collision, aggregation, or fusion.59... 

Micellization is a second-order or continuous type phase transition. Therefore, one observes continuous changes over the course of micelle fonnation. Many experimental teclmiques are particularly well suited for examining properties of micelles and micellar solutions. Important micellar properties include micelle size and aggregation number, self-diffusion coefficient, molecular packing of surfactant in the micelle, extent of surfactant ionization and counterion binding affinity, micelle collision rates, and many others. 

Note that flocculation is a purely physical process in which the treated water is gently stirred to increase interparticle collisions and, thus, promote the formation of large particles. After adequate flocculation, most of the aggregates will settle out during the 1 to 2 hours of sedimentation. 

Each process can give rise to collisions, hence has the potential of causing aggregation leading to secondary agglomeration. These processes are illustrated in Figures 6.6(a) and (b) respectively. 

Thus under ideal circumstances the modes of aggregation can be discriminated by such plots. Deviations below the expected slopes are usually attributed to collision inefficiency leading to imperfect aggregation. In a crystallization or precipitation process, of course, deviations may also occur due to growth and nucleation unless properly accounted for. 

In addition to bulk liquid turbulence effects, suspended particles maybe involved in collisions with one another or with solid surfaces within the vessel. This phenomenon has been extensively studied in micro-carrier cultures [60] and appears to be significant at high concentrations [61]. Rosenberg [69] and Meijer [72] applied the approach of Cherry and Papoutsakis [60] to the study of collision phenomena involving spherical plant cell aggregates of 190 and 100 pm, respectively. In both cases it was concluded that for typical biomass concentrations, particle-particle interactions were of less significance than particle-impeller collisions. 

Enhanced particle aggregation by tiny bubble bridging, giving rise to increased collision probability of the enlarged particle aggregates with flotation-sized bubbles... 

In the ideal collision free environment of a molecular beam, the properties of a metal cluster can be considered to be truely isolated from cluster-substrate effects. Therefore, spectroscopic methods that can selectively extract information from metal cluster beams hold great promise for illuminating diverse size dependent properties of aggregates of metal atoms in their equilibrium configuration (23). 

Because polymer adsorption is effectively irreversible, and because adsorption and floe growth occur simultaneously, flocculation is a non-equilibrium process. As a result, performance is largely determined by the kinetics of adsorption and aggregation. Both of these can be regarded as collision processes involving solid particles and polymer molecules. In each case, collisions can arise due to either Brownian motion or agitation of the suspension. The collision frequency v between particles and polymer molecules can be estimated from °... 

Destabilisation of the dispersion to permit particle-particle collisions and aggregate formation. 

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